1. Field of the Invention
The invention generally relates to a control valve for a fuel injector and, more particularly, to a piezoelectric control valve for a hydraulically actuated fuel injector.
2. Background Description
There are many types of fuel injectors designed to inject fuel into a combustion chamber of an engine. For example, fuel injectors may be mechanically, electrically or hydraulically controlled in order to inject fuel into the combustion chamber of the engine. In the hydraulically actuated systems, a control valve body may be provided with two, three or four way valve systems, each having grooves or orifices which allow fluid communication between working ports, high pressure ports and venting ports of the control valve body of the fuel injector and the inlet area. The working fluid is typically engine oil or other types of suitable hydraulic fluid which is capable of providing a pressure within the fuel injector in order to begin the process of injecting fuel into the combustion chamber.
In current designs, a driver will deliver a current or voltage to an open side of an open coil solenoid. The magnetic force generated in the open coil solenoid will shift a spool into the open position so as to align grooves or orifices (hereinafter referred to as “grooves”) of the control valve body and the spool. The alignment of the grooves permits the working fluid to flow into an intensifier chamber from an inlet portion of the control valve body (via working ports). The high pressure working fluid then acts on an intensifier piston to compress an intensifier spring and hence compress fuel located within a high pressure chamber. As the pressure in the high pressure chamber increases, the fuel pressure will begin to rise above a needle check valve opening pressure. At the prescribed fuel pressure level, the needle check valve will shift against the needle spring and open the injection holes in a nozzle tip. The fuel will then be injected into the combustion chamber of the engine.
However, in such a conventional system, a response time between the injection cycles may be slow thus decreasing the efficiency of the fuel injector. Also, injection events may vary in duration. This is mainly due to the slow movement of the control valve spool. More specifically, the slow movement of the control valve spool may result in a slow activation response time to begin the injection cycle. To remedy this inadequacy, additional pressurized working fluid may be needed; however, additional energy from a high pressure oil pump must be expanded in order to provide this additional working fluid. This leads to inefficiency in the operations of the fuel injector, itself. Also, the working fluid at an end of an injection cycle may not be vented at an adequate response rate due to the slow movement of the control valve spool.
A solution to the foregoing problems is the utilization of a piezoelectric actuator system as disclosed in co-pending U.S. patent application Ser. No. 10/638,322. In this system many advantages over the related art systems are provided such as, for example, providing a short control valve stroke. This shorter stroke translates into a fast response time for outflow of the inlet rail pressure, thereby the fuel injector has an increased efficiency over the related art. Further control features can be provided to fuel injectors in order to provide even greater advantages and efficiencies over known related art systems.